Passing Map to Jaspersoft studio report

Hello,

I am trying to pass data i got from severals Databases in Java to a Jasper Report via Rest.
Putting the query in the report is not possible and I do not want to create dependencies between Java and Jaspersoft. I then figured I could pass the data under the form of a Map or even a List of Map.
It however give me an error. I can already generate several reports and all simple parameters types like String and Integer work.

I am using Ubuntu and Jaspersoft studio 6.3.1 final

Here is my setup:

The next picture depict how i get the map on Jaspersoft studio. the $P{REPORT_PARAMETERS_MAP} is to see what the map look like in his textual form

This is the error (in java) that is caused during the generation of the report:

If i remove the box that query the map, the report generate correctly and provdide me with the textual representation of the map.

The same textual representation is generated if i set Is Prompting = true and generate the map manually in the preview. The main difference beeing that with the preview, it work.

I'd be grateful for any help you can offer.

-Marc-André